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130 lines
2.9 KiB
Groff
130 lines
2.9 KiB
Groff
.\" Generated by Mmark Markdown Processer - mmark.miek.nl
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.TH "COREDNS-K8S_EXTERNAL" 7 "December 2019" "CoreDNS" "CoreDNS Plugins"
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.SH "NAME"
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.PP
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\fIk8s_external\fP - resolves load balancer and external IPs from outside Kubernetes clusters.
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.SH "DESCRIPTION"
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.PP
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This plugin allows an additional zone to resolve the external IP address(es) of a Kubernetes
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service. This plugin is only useful if the \fIkubernetes\fP plugin is also loaded.
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.PP
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The plugin uses an external zone to resolve in-cluster IP addresses. It only handles queries for A,
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AAAA and SRV records; all others result in NODATA responses. To make it a proper DNS zone, it handles
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SOA and NS queries for the apex of the zone.
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.PP
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By default the apex of the zone will look like the following (assuming the zone used is \fB\fCexample.org\fR):
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.PP
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.RS
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.nf
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example.org. 5 IN SOA ns1.dns.example.org. hostmaster.example.org. (
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12345 ; serial
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14400 ; refresh (4 hours)
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3600 ; retry (1 hour)
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604800 ; expire (1 week)
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5 ; minimum (4 hours)
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)
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example.org 5 IN NS ns1.dns.example.org.
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ns1.dns.example.org. 5 IN A ....
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ns1.dns.example.org. 5 IN AAAA ....
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.fi
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.RE
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.PP
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Note that we use the \fB\fCdns\fR subdomain for the records DNS needs (see the \fB\fCapex\fR directive). Also
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note the SOA's serial number is static. The IP addresses of the nameserver records are those of the
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CoreDNS service.
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.PP
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The \fIk8s_external\fP plugin handles the subdomain \fB\fCdns\fR and the apex of the zone itself; all other
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queries are resolved to addresses in the cluster.
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.SH "SYNTAX"
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.PP
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.RS
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.nf
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k8s\_external [ZONE...]
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.fi
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.RE
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.IP \(bu 4
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\fBZONES\fP zones \fIk8s_external\fP should be authoritative for.
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.PP
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If you want to change the apex domain or use a different TTL for the returned records you can use
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this extended syntax.
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.PP
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.RS
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.nf
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k8s\_external [ZONE...] {
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apex APEX
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ttl TTL
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}
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.fi
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.RE
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.IP \(bu 4
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\fBAPEX\fP is the name (DNS label) to use for the apex records; it defaults to \fB\fCdns\fR.
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.IP \(bu 4
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\fB\fCttl\fR allows you to set a custom \fBTTL\fP for responses. The default is 5 (seconds).
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.PP
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Enable names under \fB\fCexample.org\fR to be resolved to in-cluster DNS addresses.
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.PP
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.RS
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.nf
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\&. {
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kubernetes cluster.local
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k8s\_external example.org
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}
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.fi
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.RE
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.PP
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With the Corefile above, the following Service will get an \fB\fCA\fR record for \fB\fCtest.default.example.org\fR with the IP address \fB\fC192.168.200.123\fR.
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.PP
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.RS
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.nf
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apiVersion: v1
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kind: Service
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metadata:
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name: test
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namespace: default
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spec:
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clusterIP: None
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externalIPs:
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\- 192.168.200.123
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type: ClusterIP
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.fi
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.RE
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.PP
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For some background see resolve external IP address
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\[la]https://github.com/kubernetes/dns/issues/242\[ra].
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And A records for services with Load Balancer IP
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\[la]https://github.com/coredns/coredns/issues/1851\[ra].
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.PP
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PTR queries for the reverse zone is not supported.
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